This application claims the priority of German Application No. 199 18 219.1, filed Apr. 22, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a service life indicator for highly stressed lightweight structures, The service life indicator has a strip of material as the test piece, which has at least one hole arranged off-center in the test piece and a notch extending from the edge of the hole in the direction of the edge of the test piece. The test piece serves as the device for determining the material fatigue. A service life indicator of this type is known from German Patent Document DE 43 38 850 A1.
From U.S. Pat. No. 3,136,154, a strip-shaped fatigue indicator is known which has holes or notches and which is mounted on the structure to be examined.
Modern military pioneering bridges are progressive light-weight aluminum constructions, characterized by a high material utilization factor, withxe2x80x94in comparison to civilian bridgesxe2x80x94very low crossing numbers and high loads. The relatively low number of guaranteed crossings requires one to record the number of crossings which occur as a function of the crossing load and the laid span in order to obtain a reliable indication before reaching the permitted service life and a measurement of the remaining surface life. This recording was previously carried out by keeping a log-book.
The following is known as prior art with respect to service life indicators of metallic structures of this type, in addition to the above-mentioned log-book. The monitoring of the structure by means of wire strain gauges, meters and a corresponding electronic analyzing system; the monitoring of the structure by means of glued-on metal foils which change their reflection behavior as the result of any extension experienced; a device which is mounted on the structure to be monitored and into which small, differently notched, test pieces are clamped.
It is disadvantageous that these indicators either: (1) require electric energy; (2) have no long-term-stable connection to the structure; (3) are too sensitive and too expensive for a constant use in the open air; and/or (4) only insufficiently take into account additional marginal conditions, such as the deviation of material and environmental influences.
The object of the invention is to provide a robust and reliably readable fatigue indicator for light-weight structures.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.